[mana]

hi all
in books the puckered or twisted conformations for cyclobutane or cyclopentane is attributed because of their torsional strain or angle strain but why cyclohexane which doesn't have any of these strain, has some puckered conformations for example chair, half chair, twisted and boat?
is it because of steric strain?

[Enthalpy]

[...]cyclohexane which doesn't have any of these strain[...]

Really? Every bond turns by 180-109.5=70.5°, so six bonds turn by 423°, not 360°. The difference is absorbed by the non-planar arrangement, which permits, in the case of cyclohexane, to absorb it well. It works rather well for cyclopentane too.

As opposed, the non-planar conformation makes the angles of cyclobutane worse, not better. I've read it results from hydrogen repulsion.